World 1-1 (Super Mario Maker for Nintendo 3DS)
From the Super Mario Wiki
World 1-1 is a Super Mario Bros.-style level, with the main area being Ground themed and the sub area being Underground themed. The level starts off with an empty plain, immediately followed by a ? Block beside a set of two ? Blocks and three Brick Blocks. The leftmost ? Block of the set of two ? Blocks and three Brick Blocks contains a Super Mushroom or Fire Flower. Under this set is a Goomba, and over it is another ? Block. After this is a two block high pipe, followed a three block high pipe and a Goomba. After this is another pipe, this one being four blocks tall. Beside this pipe are two Goombas and a four block tall enterable Warp Pipe. Upon entering this Warp Pipe, Mario will arrive in an underground bonus room with many coins and Brick Blocks everywhere. To the right of the room is a sideways Warp Pipe with a One-Way Wall facing at its entrance so the player can't enter it from the main section of the level. Entering this Warp Pipe will lead the player back to the overworld, at the second last pipe, essentially skipping the level. If Mario were to skip the initial Warp Pipe, he'd find a pit with a Hidden Block containing a 1-Up Mushroom to the left of it. Past this is a ? Block containing a Super Mushroom or Fire Flower in the middle of two Brick Blocks. Over this is a set of eight Brick Blocks with two Goombas on top of them. After another pit will be a Coin Block with three Brick Blocks and a ? Block over it. Two Goombas will march below, followed by two Brick Blocks, rightmost containing a Super Star. After this are three ? Blocks with two block wide gaps in between and another ? Block over them with a Super Mushroom or Fire Flower. Under them is a green Koopa Troopa followed by two Goombas and a lone Brick Block with a set of three Brick Blocks over it. Past these are two sets of two Goombas, which have a set of two Brick Blocks and a set of two ? Blocks along with two more Brick Blocks over them. Following this is a Hard Block staircase with a small gap leading to another Hard Block staircase. The pit below is covered up by land. After this is another Hard Block staircase leading to a Hard Block staircase, this time with an actual pit in between. Past this is a two block tall Warp Pipe, (which is where Mario exits from the underground secret area) followed by a set of three Brick Blocks with a ? Block in between. Past this are two Goombas and another two block tall pipe, immediately followed by a big Hard Block staircase leading to the Goal Pole.
In the underground bonus room, it's possible to leave the underground section and return to the place where the hidden 1-Up Mushroom is found by going through the Warp Pipe on the ceiling, though this takes skill and Mario being in his Super Mario form.